THE PHOTO REPAIR OF PYRIMIDINE DIMERS BY DNA PHOTOLYASE AND MODEL SYSTEMS

Pyrimidine dimers are eliminated from DNA by a number of different mechanisms known as DNA repair. Photoreactivation, the reversal of the harmful effects of short wavelength radiation by subsequent exposure to longer wavelengths, is one such mechanism. In photoreactivation, the enzyme DNA photolyase utilises light in order to catalyse the cleavage of the cyclobutane ring of the pyrimidine dimer. The results of recent studies of E. coli DNA photolyase and model systems using techniques such as steady state and flash photolysis, time resolved fluorescence and photo CIDNP are surveyed. A mechanism is proposed for the in vitro reaction of E. coli DNA photolyase which involves photoreduction of the FAD radical cofactor followed by electron donation to the dimer from the excited singlet state of reduced FAD.